Django aggregate query generating SQL error
- by meepmeep
I'm using Django 1.1.1 on a SQL Server 2005 db using the latest sqlserver_ado library.
models.py includes:
class Project(models.Model):
name = models.CharField(max_length=50)
class Thing(models.Model):
project = models.ForeignKey(Project)
reference = models.CharField(max_length=50)
class ThingMonth(models.Model):
thing = models.ForeignKey(Thing)
timestamp = models.DateTimeField()
ThingMonthValue = models.FloatField()
class Meta:
db_table = u'ThingMonthSummary'
In a view, I have retrieved a queryset called 'things' which contains 25 Things:
things = Thing.objects.select_related().filter(project=1).order_by('reference')
I then want to do an aggregate query to get the average ThingMonthValue for the first 20 of those Things for a certain period, and the same value for the last 5.
For the first 20 I do:
averageThingMonthValue = ThingMonth.objects.filter(turbine__in=things[:20],timestamp__range="2009-01-01 00:00","2010-03-00:00")).aggregate(Avg('ThingMonthValue'))['ThingMonthValue__avg']
This works fine, and returns the desired value.
For the last 5 I do:
averageThingMonthValue = ThingMonth.objects.filter(turbine__in=things[20:],timestamp__range="2009-01-01 00:00","2010-03-00:00")).aggregate(Avg('ThingMonthValue'))['ThingMonthValue__avg']
But for this I get an SQL error: 'Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.'
The SQL query being used by django reads:
SELECT AVG([ThingMonthSummary].[ThingMonthValue]) AS [ThingMonthValue__avg]
FROM [ThingMonthSummary]
WHERE ([ThingMonthSummary].[thing_id] IN
(SELECT _row_num, [id] FROM ( SELECT ROW_NUMBER() OVER ( ORDER BY [AAAA].[id] ASC) as _row_num,
[AAAA].[id] FROM ( SELECT U0.[id] FROM [Thing] U0 WHERE U0.[project_id] = 1 ) AS [AAAA]) as QQQ
where 20 < _row_num) AND [ThingMonthSummary].[timestamp] BETWEEN '01/01/09 00:00:00' and '03/01/10 00:00:00')
Any idea why it works for one slice of the Things and not the second? I've checked and the two slices do contain the desired Things correctly.
